(1) Field of the Invention
This invention relates to a process for preparation of capsule for use in isostatic pressing treatment, such as the hot isostatic pressing process (HIP process) and the warm isostatic pressing process (WIP process), which are utilized for producing a sintered body of high density through exerting a high hydraulic pressure on a material to be treated, such as a molded powder body of ceramic, metal, resin or the like, at high temperature, or utilized for diffusion joining of two or more different materials through exerting a high hydraulic pressure on the materials at high temperature.
(2) Description of the Prior Art
The HIP and WIP processes, in which compression molding is carried out by using a fluid having a high pressure of from several hundreds to several thousands of kilograms-force per square centimeters (kgf/cm.sup.2) as a pressure medium at high temperature, have been rapidly coming into increasingly wider use in recent years as a technique for sintering of difficultly processible powder materials into high-density products or as a technique for solid phase diffusion joining, because the processes provide high working pressures and enable isostatic compression.
The HIP process uses a high-pressure gas as a pressure medium and, therefore, makes it possible to generate a high temperature of 2000.degree. C. or above. On the other hand, the WIP process employs a heat-resistant oil or the like, and permits the use of temperatures up to about 300.degree. C. at most.
In the case of sintering a powder material into a high-density mass or performing solid phase diffusion joining, both the above two processes require a pretreatment for covering the entire surface of the material to be treated by a gas-impermeable material so as to prevent the penetration of the pressure medium into the material being treated.
As a method for the pretreatment, a method in which the material to be treated, comprising a powder material or the like, is sealed in a metallic container, or capsule, in a vacuum condition, as for example disclosed in Japanese Patent Application Laid-Open (KOKAI) No. 47-16308 (1972) or 57-116702 (1982).
According to the technique disclosed in the Japanese Patent Application Laid-Open (KOKAI) No. 47-16308 (1972), as shown in FIG. 11 an alternate stack of plate-like materials 101 to be treated and metallic foils 102 is sealed in a metallic capsule 107 comprising a pipe member 103, a bottom portion 104 and a cap 106 having a vacuum pipe 105. The pipe member 103, bottom portion 104 and the cap 106 are welded to each other. After evacuation of the welded assembly through the vacuum pipe 105, the pipe 105 is mechanically compressed to seal up the pipe 105, and then the pipe 105 is cut off at the sealed portion. Finally, the cut portion of the vacuum pipe 105 is sealed up by welding, fusion bonding or the like to prepare a capsule 107 in which the materials 101 to be treated are contained in the evacuated condition.
The capsule 107 thus prepared is fed into a furnace of an HIP device, to be subjected to an HIP treatment under predetermined conditions. Then, the capsule 107 is removed, and the foils 102 are taken away, to obtain plate-like sintered products.
According to the technique disclosed in the Japanese Patent Application Laid-Open (KOKAI) No. 57-116702 (1982), as shown in FIG. 12 a material 101 to be treated is placed in a metallic capsule 107 comprising a pipe member 109, a lower cap 110 and the like, and the space between the material 101 and the capsule 107 is filled up with powder particles 111 having fluidity. The capsule 107 is evacuated through a pipe 112, and an intermediate portion of the pipe 112 is hermetically closed for sealing, followed by an HIP treatment.